The German leads their FedEx ATP Head2Head series 7-2. Kohlschreiber, who won the Auckland title in 2008, will play Tennys Sandgren of the U.S. to return to the ATP 250 final.

Sandgren didn't face a single break point and slid past Argentina's Leonardo Mayer 6-3, 7-6(5). The 27-year-old American delivered 11 aces and won 83 per cent of his first-serve points.

Sandgren reached the quarter-finals of the Australian Open last year, and 44 per cent of his ATP Rankings points (360/814) are from that two-week stretch in Melbourne.

“It's important because I have a lot of points falling off this month,” Sandgren said, before laughing, about reaching the semi-finals in New Zealand. “I worked really hard in November, December to try and just put myself in a position to play well to start the year, and I'm happy that's the case so far.”

In the top half of the draw, Auckland native Cameron Norrie ousted American Taylor Fritz 7-6(3), 6-3. Norrie, a wild-card entry, saved all four break points and hit 11 aces en route to his fourth ATP Tour semi-final.

Germany’s Jan-Lennard Struff held his nerve in an epic three-hour battle to reach his first ATP Tour semi-final since September 2017 at the St. Petersburg Open (l. to Dzumhur). Struff fired 22 aces past fourth-seeded Spaniard Pablo Carreno Busta, who saved 13 of 15 break points, in a 7-6(5), 6-7(6), 7-6(7) victory. Last season, Struff went 0-4 in quarter-finals.

Struff needed nine set point chances to clinch the first set and six match point opportunities in the decider, which also included saving one match point for Carreno Busta at 5/6 in the third set tie-break.